Thymoquinone derivatives for treatment of cancer

ABSTRACT

The present invention describes thymoquinone compounds formula (I): (i) These compounds have been identified as being useful in the treatment of cancer.

TECHNICAL FIELD

This invention relates to substituted thymoquinone derivatives. The invention also relates to the use of such compounds in the treatment of cancer and pharmaceutical compositions containing such compounds.

SEQUENCE LISTING

This application contains a sequence listing. The sequence listing file in ASCII text format is named Sequence_Listing_140943_ST25.txt, is 876 bytes in size, was created on Jun. 19, 2017, and is incorporated herein by reference in its entirety.

BACKGROUND ART

Thymoquinone, 2-isopropyl-5-methyl-1,1,4-benzoqinone (TQ), can be extracted from black seed (Nigella sativa) oil and has been reported as an anticancer agent in cancer cells. The anticancer effects of TQ on malignant tumours with selectivity towards cancer cells over normal cell has been discussed in Aggarwall B B et al (2008) Planta Med vol. 74(13) pp 1560-1569. Thymoquinone analogs have also been proposed for the use in treating pancreatic cancers, for example in WO2011126544.

The end caps of human chromosomes, telomeres, are known to protect DNA chromosomes against degradation, non-homologous end-stacking and nuclease attacks. Telomeres are shortened after each cell division till the cell loses its functions and apotosis. The telomerase enzyme, found active in most cancer cells, re-elongates the telomere and maintains its length causing cancer cell to continue to divide indefinitely. Telomeres comprise tandem repeats enriched in guanine bases that fold up in physiological conditions to form four-stranded DNA called G-quadruplex. Folding single stranded telomeric DNA into G-quadruplex structure has been shown to inhibit the telomerase enzyme, overexpressed in cancer cells.

Small molecules that bind and stabilise G-quadruplex DNA have been found to inhibit the telomerase enzyme in cancer cells and subsequently inhibit DNA replication and cancer cell proliferation, Huppert J L (2007), Phil. Trans. A. Math. Phys. Eng. Sci., vol. 365(1861) pp 2969-2984. Therefore molecules with high preferential affinity towards G-quadruplex DNA have been seen as a potential avenue of compounds for developing new anticancer therapeutic agents.

Accordingly it is an object of the invention to provide further thymoquinone derivatives that may be effective in cancer treatment.

SUMMARY OF INVENTION

The present invention relates to compounds of formula (I):

and to pharmaceutically salts or solvates thereof wherein: R₁ and R₂ are independently selected from C₁-C₆ alkyl, wherein R₁ and R₂ are different; X is NR₃R₄, wherein:

-   -   R₃ is selected from H or —(CH₂)₂—OH; and     -   R₄ is selected from H or —(C₁-C₄alkyl)R₅, wherein:         -   R₅ is selected from:         -   a) —OH,         -   b) phenyl, wherein phenyl is optionally substituted by 1-3             substituents independently selected from —CF₃, —F, —OCH₃,             —NH₂ and —SO₂NH₂,         -   c) a 5 or 6 membered heterocyclic ring having 1 or 2 hetero             atoms selected from O and N, and wherein the heterocyclic             ring is optionally substituted by 1-2 substituents             independently selected from —OH and CH₃,         -   d) a ring system having the formula of:

-   -   -    and         -   e) NR₆R₇, wherein:             -   R₆ is selected from H or CH₃; and             -   R₇ is selected from CH₃, phenyl, and a ring system                 having the formula of:

-   -   -   -   wherein the ring system is optionally substituted by 1-2                 substituent of CH₃; and                 Y is H.

In a preferred embodiment R₁ is CH₃, or isopropyl. More preferably R₁ is CH₃.

In a preferred embodiment R₂ is CH₃, or isopropyl. More preferably R₂ is isopropyl.

In a particularly preferred embodiment R₁ is CH₃ and R₂ is isopropyl.

In a preferred embodiment R₃ is H.

In a preferred embodiment R₄ is —(C₁-C₄alkyl)R₅. More preferably R₄ is —(C₁-C₂alkyl)R₅.

In a preferred embodiment R₅ is selected from:

-   -   a) —OH,     -   b) phenyl, wherein phenyl is optionally substituted by 1-3         substituents independently selected from —CF₃, —F, —OCH₃, —NH₂         and —SO₂NH₂,     -   c) a 5 or 6 membered heterocyclic ring selected from         morpholinyl, pyranyl, piperidinyl, pyrrolidinyl, piperazinyl,         pyridinyl, and pyrimidinyl, wherein the heterocyclic ring is         optionally substituted by 1-2 substituents independently         selected from —OH and CH₃.     -   d) a ring system having the formula of:

-   -    and     -   e) NR₆R₇, wherein:         -   R₆ is selected from H or CH₃; and         -   R₇ is selected from CH₃, phenyl, and a ring system having             the formula of:

-   -   -   wherein the ring system is optionally substituted by 1-2             substituent of CH₃.

In one embodiment wherein R₅ is a 5 or 6 membered heterocyclic ring, the 5 or 6 membered heterocyclic ring is selected from morpholinyl, pyranyl, piperidinyl, pyrrolidinyl, piperazinyl, each optionally substituted by —OH or the heterocyclic ring is selected from pyridinyl, and pyrimidinyl, wherein the pyrimidinyl is optionally substituted with —OH and CH₃.

In a particularly preferred embodiment R₄ is H or —(C₁-C₂alkyl)R₅, wherein R₅ is selected from OH, morpholinyl and phenyl, wherein the phenyl is optionally substituted with 1 or 2 substituents selected from —CF₃, —F and —OCH₃.

In one embodiment when R₃ is H, R₄ is preferably H or —(C₁-C₂alkyl)R₅, wherein R₅ is selected from morpholinyl and phenyl, wherein the phenyl is optionally substituted with 1 or 2 substituents selected from —CF₃, —F and —OCH₃.

Particularly preferred compounds of the invention include:

-   5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone -   5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone -   5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone -   5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone -   5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone -   5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone -   5-isopropyl-2-methyl-3-(3,4-dimethoxylbenzylamino)-1,4-benzoquinone -   3-amino-5-isopropyl-2-methyl-1,4-benzoquinone.

A particularly preferred compound is 3-amino-5-isopropyl-2-methyl-1,4-benzoquinone.

Suitable salts include salts of acidic or basic groups present in compounds of formula (I). The compounds of formula (I) that are basic in nature are capable of forming a wide variety of salts with various inorganic and organic acids. The acids that may be used to prepare pharmaceutically acceptable acid addition salts of such basic compounds of formula (I) are those that form non-toxic acid addition salts. Suitable salts include acetate, benzensulfonate, benzoate, bicarbonate, bisulfate, bitartrate, borate, bromide, calcium edentate, camsylate, carbonate, chloride, clavulanate, citrate, dihydrochloride edentate, edisylate, estolate, esylate, ethylsuccinate, fumarate, gluceptate, gluconate, glutamate, glycollylarsanilate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride, iodide isothionate, lactate, lactobionate, laurate, malate, maleate, mandelate, mesylate, methylsulfate, mucate, napsylat, nitrate, oleate, oxalate, pamoate, palmitate, pantothenate, phosphate, diphosphate, diphosphate, polygalacturonate, salicylate, stearate, subacetate, succinate, tannate, tartrate, teoclate, tosylate and valerate.

The compounds of the present invention may be synthesised by a number of synthetic routes. In one method of making the compounds of the invention, thymoquinone derivatives can be synthesised as shown in Scheme I, wherein R₁, R₂, R₃ and R₄ are defined herein.

Compounds of formula (I) may be synthesised in a one pot reaction by reacting thymoquinone in a suitable solvent such as methanol, with the appropriate amine, NHR₃R₄, dissolved in a suitable solvent. The mixture is reacted in the presence of air at room temperature. The solvent is then concentrated and purified and the resultant products are crystallised.

An alternative route for synthesising a thymoquinone derivative of formula (III) is shown in scheme (II).

Compounds of formula (III) may be synthesised by reacting thymoquinone with dimethoxybenzylamine in a solvent, such as methanol. The mixture is reacted in the presence of air at room temperature resulting in the formation of a compound of formula (IV). The mixture is allowed to decompose and a product of formula (III) is formed. The solvent is then concentrated and purified and the resultant product is crystallised.

These compounds have been found to selectively bind G-quadruplex DNA and stabilise their structure. Stabilisation of the G-quadruplex structure can inhibit the telomerase enzyme, and therefore the compounds may play a role in the treatment of cancer.

The invention also relates to compounds of formula (I) as described above for use in the treatment of cancer. In particular the compounds are particularly useful in the treatment of pancreatic cancer, lung cancer, prostate cancer and breast cancer.

The invention also provides a method of treating cancer in a mammal, particularly a human, comprising administering to the mammal an amount of a compound of formula (I) as defined above, or a pharmaceutically acceptable salt or solvate thereof. The compound may be administered in a therapeutically effective amount.

The invention further relates to the compounds of formula (I) in combination with at least one suitable anti-tumour or neoplastic agent for the treatment of cancer, in particular for the treatment of pancreatic, lung, prostate or breast cancer.

The term “treatment” is intended to include curing, reversing, alleviating, palliative and prophylactic treatment of the condition.

A “therapeutically effective amount” of a compound is an amount of the compound, which when administered to a subject, is sufficient to confer the intended therapeutic effect. A therapeutically effective amount can be given in one or more administrations.

Common cancers would include, bladder, breast, colon, rectal, endometrial, kidney (renal cell), leukaemia, lung, melanoma, non-Hodgkin lymphoma, pancreatic, prostate, brain, skin, liver and thyroid cancers.

Patients suffering from cancer are commonly co-administered additional therapeutic agents, in particular suitable antineoplastic or anti-tumour agents. Suitable co-administrants would include:

1. Alkylating antineoplastic agents: such as cisplatin, carboplatin, oxaliplatin, mechlorethamine, cyclophosphamide, chlorambucil, and ifosfamide.

2. Plant alkaloids and terpenoids. These include:

-   -   i. vinca alkaloids such as vincristine, vinblastine, vinorelbine         and vindesine     -   ii. podophyllotoxins such as etoposide and teniposide     -   iii. taxanes, such as paclitaxel, originally known as taxol, and         docetaxel.         3. Topoisomerase inhibitors:     -   i. type I topoisomerase inhibitors include camptothecins:         irinotecan and topotecan     -   ii. type II inhibitors include amsacrine, etoposide, etoposide         phosphate, and teniposide         4. Cytotoxic antibiotics such as actionmycin, anthracyclins,         doxorubicin, daunorubicin, valrubicin and epirubicin. Other         cytoxic antibiotics include bleomycin, plicamycin and mitomycin.

Other therapeutic agents are commonly administered to patients to deal with the side effects of chemotherapy. Such agents might include anti-emetics for nausea, or agents to treat anaemia and fatigue. Other such medicaments are well known to physicians and those skilled in cancer therapy.

Such agents may be administered sequentially, simultaneously or concomitantly.

The invention also relates to a pharmaceutical composition comprising a compound of formula (I) as described above, or a pharmaceutically acceptable salt or solvate thereof and a pharmaceutically acceptable diluents or carrier.

The pharmaceutical composition may comprise an additional therapeutic agent.

Suitable composition forms include forms suitable for oral administration such as tablets, capsule, pills, powders, sustained release formulations, solutions, and suspension, for parental injection such as sterile saline solutions, suspensions or emulsion; for topical administration such as ointments or creams; or rectal administration such as suppositories.

Exemplary parenteral administration forms include suspensions or solutions in sterile aqueous solutions, for example aqueous propylene glycol or dextrose solutions. Such dosage forms can be suitably buffered, if desired.

Suitable pharmaceutical carriers include inert diluents or fillers, water and various organic solvents. Compositions may also include additional ingredients such as flavouring, binders, and excipients. Tablets may include: disintegrates such as starch, alginic acid and complex silicates; binding agents such as sucrose, gelatine and acacia, and lubricating agents such as magnesium stearate, sodium lauryl sulphate and talc.

Solid compositions may also include soft and hard gelatin capsules. Preferred materials include lactose, milk sugars and high molecular weight polyethylene glycols.

Aqueous suspensions or elixirs may include sweetening or flavouring agents, colours and dyes, emulsifying agents, suspending agents as wells as diluents such as water, ethanol, propylene glycol, glycerin or combinations thereof.

Pharmaceutical forms suitable for the delivery of the compounds of the present invention and methods of preparing the various pharmaceutical compositions will be readily apparent to those skilled in the art. Such compositions and methods for their preparations may be found, for example in Remington's Pharmaceutical Sciences, 19^(th) Edition (Mack Publishing Company 1995).

FIGURES

FIGS. 1A and 1B shows inhibition of cellular viabilities by compounds TQ 1-5 in A540 cells (FIG. 1A) and TQ8 in A549, MDA-MB-231, and HT29 cells (FIG. 1B). Cells were treated at the indicated concentrations of compounds TQ 1-5 and 8 or with vehicle (0.1% DMSO) as a control. Columns, mean; bars S.E.M.

FIG. 2 shows fluorescence titrations of compounds TQ1-8 (5×10−6M) (a-h respectively) with G-quadruplex. TQs were excited at 279, 280, 280, 278, 280, 280, 280 and 327 nm respectively with 10 nm slits width. The inset represents a plot for fluorescence titrations using modified Scatchard equation.

FIG. 3 shows the fluorescence spectra of 5′-Flu-G-quadruplex (2×10−6 M) with compounds TQ1-8. 5′-Fl-G-quadruplex was excited at 494 nm and emitted at 518 nm.

FIG. 4 shows the CD spectra of G-quadruplex (4×10⁻⁶ M) with compounds TQ1-8 (a-h respectively).

FIG. 5 shows the melting curve for G-quadruplex DNA and its complexes with compounds TQ1-8.

FIG. 6 shows the selectivity of compounds TQ1-8 toward G-quadruplex (5′-Flu-TelQ, 1×10−7 M) in presence of 0, 10, 50 and 100 folds of ct-DNA (A) and telomere dsDNA (B).

EXPERIMENTAL

The synthesis of various compounds of the present invention is described by way of example.

Synthesis of Thymoquinone Derivatives

5 mmol thymoquinone (821 mg) (Frinton Laboratories Inc, USA) was dissolved in methanol (50 mL) into a two necks flask (100 mL). The amine solution (5 mmol), (2-aminoethylmorpholine, benzylamine, 4-(trifluoromethyl) benzylamine, 3,5-bis(trifluoromethyl)benzylamine, 3,4-dimethoxybenzylamine, 4-fluorobenzyl-amine or 2-aminoethanol (Sigma-Aldrich)), dissolved in methanol (5 mL), was added drop wise to the thymoquinone solution.

The reaction mixture was stirred and air bubbled at room temperature for up to 3 days during which the reaction progress was monitored using TLC. The solvent was concentrated under vacuum and the product was purified on silica gel column using hexane:ethyl acetate (6:4 v/v) as mobile phase.

This general procedure was applied for the synthesis of compounds TQ1-TQ7. Compound 3-aminothymoquinone (TQ8) was prepared as described below.

3-aminothymoquinone (TQ8) was synthesized by allowing thymoquinone (5 mmol, 821 mg) to react with 3,4-dimethoxybenzylamine (5 mmol, 777 μL) in methanol (5 mL) as per the procedure above. The solution was stirred and air bubbled at room temperature for 5 days during which the reaction was monitored by TLC.

Initially, 3′,4-dimethoxybenzylamino-thymoquinone (TQ7) is formed and then hydrolyzed to form 3-aminothymoquinone (TQ8). Oxidation of 3′, 4-dimethoxybenzylamino-thymoquinone (TQ7) results in the formation of the hydroxymethyl-amino intermediate which upon rearrangement produced 3-aminothymoquinone (TQ8) and 3,4-dimethoxybenzaldehyde.

The solvent was concentrated under vacuum followed by purifying the product over silica gel column using hexane:ethyl acetate (7:3 v:v) as mobile phase. The pink layer was separated into two layers, the first released is for TQ7 and the second released is for TQ8. R_(f) for the compound TQ8 is 0.662.

The mechanism for the formation of 3-aminothymoquinone (TQ8) is shown in Scheme (III).

The obtained products were crystallized from the same solvent and their structure was confirmed using IR, ¹H-NMR and ¹³C-NMR, MS spectrometry and elemental analysis. Table 1 shows the reaction times, melting points and reaction yields of the newly synthesized thymoquinone amine derivatives.

Reaction times between 24 hours and 5 days were found necessary for different products with melting temperatures of 68-114° C. and reaction yields between 45.2-73.8% obtained.

TABLE 1 Reac- Com- tion pound Aryl-amine Time M.P. ° C. Yield TQ1

48 hrs 92-95 68.3% TQ2

64 hrs 110.5- 112 50.1% TQ3

72 hrs   80-82.5 45.2% TQ4

72 hrs   83-84.5 73.6% TQ5

48 hrs 111-114 47.2% TQ6

36 hrs Oil 66.7% TQ7 TQ8

24 hrs  5 days Oil 68-72 61.1% 52.3%

The results of the elemental and spectral analyses of the synthesized thymoquinone derivatives (TQ1-TQ8) are provided below:

Example 1: 5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone (TQ1)

The compound of example 1 (TQ1) was separated by silica gel column chromatography using hexane/ethyl acetate 6:4 as a mobile phase.

R_(f) for the product is 0.235. It was obtained as dark violet crystals after 48 hrs, yield 68.3%, mp 92-95° C.; IR (KBr, ν cm⁻¹): 3306 (N—H), 1650 and 1615 (C═O), 1118 (C—O—C); 1H NMR (400 MHz, DMSO-d₆) δ ppm 1.03 (6H, d, J=6.8 Hz) 1.93 (3H, s) 2.36 (4H, t, J=4.6 Hz) 2.47 (2H, t, J=6.8 Hz) 2.85 (1H, m) 3.50-3.56 (6H, m) 6.27 (1H, t, J=5.6 Hz) 6.33 (1H, s); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 10.07, 21.56, 26.44, 41.24, 53.32, 57.83, 66.7, 107.81, 132.7, 145.58, 149.79, 184.73, 185.69. EI-MS: m/z 292.2, 0.9% (M⁺), 232.1, 23.1%, 206.1, 61.1%, 149.0, 67.6%, 100, 100%. Elemental analysis (C₁₆H₂₄N₂O₃), calculated: C, 65.73%; H, 8.27%; N, 9.58%. Found: C, 66.57%; H, 8.72%; N, 8.59%.

Example 2: 5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone (TQ2)

The compound of example 2 (TQ2) was purified by silica gel column chromatography using hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.485. It was obtained as dark red crystals after 64 hrs, yield 50.1%, mp 110.5-112° C.; IR (KBr, ν cm⁻¹): 3313 (N—H), 1666 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d, J=6.8 Hz) 1.77 (3H, s) 2.84 (1H, m) 4.72 (2H, d, J=7.6 Hz) 6.31 (1H, s) 7.08 (1H, t, J=7.4 Hz) 7.44 (2H, d, J=8.0 Hz) 7.68 (2H, d, J=8.4 Hz); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.81, 21.44 26.41, 47.24, 108.24, 125.78, 125.81, 127.47, 127.99, 132.19, 145.36, 146.22, 150.07, 184.78, 185.69. EI-MS: m/z 337.3, 94.4% (M⁺), 322.2, 24.1%, 192.1, 100%, 178.1, 46.3%, 159.0, 46.3%. Elemental analysis (C₁₈H₁₈F₃NO₂), calculated: C, 64.09%; H, 5.38%; N, 4.15%, Found: C, 65.15%; H, 5.34%; N, 3.76%.

Example 3: 5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone (TQ3)

The compound of example 3 (TQ3) was separated by silica gel column chromatography using hexane/ethyl acetate 7:3 as a mobile phase.

R_(f) for the product is 0.530. It was obtained as dark red crystals after 72 hrs, yield 45.2%, mp 80-82.5° C.; IR (KBr, cm⁻¹): 3315 (N—H), 2967, 1667 and 1650 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d, J=6.4 Hz) 1.79 (3H, s) 2.84 (1H, m) 4.61 (2H, d, J=6.4 Hz) 6.30 (1H, s) 6.95 (1H, t, J=8.0 Hz) 7.13 (2H, t, J=8.0 Hz) 7.25 (2H, t, J=8.0 Hz); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.88, 21.45, 26.42, 46.91, 108.14, 115.55, 115.76, 128.74, 128.82, 132.29, 137.22, 145.35, 150, 160.34, 162.75, 184.81, 185.71. EI-MS: m/z 287.2, 100% (M+), 272.2, 35.2%, 192.1, 46.3%, 178.1, 57.4%, 109.0, 97.2%. Elemental analysis (C₁₇H₁₈FNO₂), calculated C, 71.06%; H, 6.31%; N, 4.87%, Found: C, 72.16%; H, 6.95%; N, 5.67%.

Example 4: 5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone (TQ4)

The compound of example 4 (TQ4) was purified by column chromatography using hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.636. It was obtained as dark red crystals after 72 hrs, yield 73.6%, mp mp 83-84.5° C.; IR (KBr, cm⁻¹): 3312 (N—H), 2966, 1665 and 1650 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d, J=6.8 Hz) 1.80 (3H, s) 2.84 (1H, m) 4.63 (2H, d, J=7.2 Hz) 6.30 (1H, s) 6.95 (1H, t, J=7.0 Hz) 7.19-7.23 (3H, m) 7.28-7.32 (2H, m); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.87, 21.44, 26.42, 47.53, 107.84, 126.74, 127.24, 128.93, 132.37, 141.08, 145.41, 149.91, 184.82, 185.69. EI-MS: m/z 269.2, 100% (M⁺), 254.2, 30.6%, 192.1, 75.0%, 178.1, 45.4%, 91.0, 81.5%. Elemental analysis (C₁₇H₁₉NO₂): calculated C, 75.81%; H, 7.11%; N, 5.2%. Found: C, 76.95%; H, 7.39%; N, 5.62%.

Example 5: 5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone (TQ5)

The compound of example 5 (TQ5) was purified by column chromatography using hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.485. It was obtained as dark red crystals after 48 hrs, yield 47.2%, mp 111-114° C.; IR (KBr, cm⁻¹): 3319 (N—H), 2974, 1677 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d, J=6.8 Hz) 1.77 (3H, s) 2.84 (1H, m) 4.76 (2H, d, J=7.6 Hz) 6.31 (1H, s) 7.02 (1H, t, J=7.2 Hz) 7.95 (3H, s) 7.96 (3H, s); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.97, 21.4, 26.41, 47.18, 109.73, 121.04, 122.44, 125.16, 127.9, 130.45, 130.78, 131.85, 145.01, 145.72, 150.38, 184.82, 185.79. EI-MS: m/z 405.2, 0% (M+), 390.2, 75.0%, 321.2, 31.5%, 242.1, 100%, 227.1, 44.4%, 192.1, 36.1%, 178.2, 21.3%, 148.1, 18.4%. Elemental analysis (C₁₉H₁₇F₆NO₂): calculated C, 56.3%; H, 4.23%; N, 3.46%. Found: C, 57.05%; H, 4.10%; N, 2.64%.

Example 6: 5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone (TQ6)

The compound of example 6 (TQ6) was purified by silica gel column chromatography using hexane/ethyl acetate 9:1 then 7:3 as a mobile phase.

R_(f) for the product is 0.524. It was obtained as dark violet gum after 36 hrs, yield 66.7%; IR (KBr, cm⁻¹): 3408.7 (N—H), 2925, 1665.4, 1649.3 (C═O); ¹H NMR (400 MHz, CHLOROFORM-d) ppm 1.09 (6H, d, J=6.4 Hz) 2.04 (3H, s) 2.95 (1H, m) 3.64 (2H, t, J=5.0 Hz) 3.82 (2H, t, J=5.2 Hz) 5.70 (1H, s) 6.39 (1H, s); ¹³C NMR (400 MHz, CHLOROFORM-d) δ ppm 10.32, 21.31, 26.51, 46.97, 61.92, 109.19, 132.88, 144.70, 149.97, 184.72, 186.89. EI-MS: m/z 223.2, 23.8% (M⁺), 192.1, 100%, 177.1, 13.8%, 149.1, 11.0%. Elemental analysis (C₁₂H₁₇NO₃): calculated: C, 64.55%; H, 7.67%; N, 6.27%; 0, 21.50%.

Example 7: 5-isopropyl-2-methyl-3-(3,4-dimethoxylbenzylamino)-1,4-benzoquinone (TQ7)

The compound of example 7 (TQ7) was purified by silica gel column chromatography using hexane/ethyl acetate 1:1 as a mobile phase.

R_(f) for the product is 0.524. It was obtained as dark red gum after 24 hrs, yield 61.1%; IR (KBr, cm⁻¹): 3394 (N—H), 2926, 1649 (C═O); ¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.08 (6H, d, J=6.8 Hz) 2.05 (3H, s) 2.94 (1H, m) 3.85 (6H, s) 4.57 (2H, d, J=3.6 Hz) 5.64 (1H, s) 6.39 (1H, s) 6.72-6.87 (3H, m); ¹³C NMR (400 MHz, Chloroform-d) δ ppm 10.27, 21.30, 26.51, 49.13, 55.88, 109.21, 110.31, 111.35, 119.48, 131.07, 132.96, 144.37, 149.28, 149.85, 184.49, 186.91. EI-MS: m/z 329.2, 0% (M⁺), 314.2, 286.1, 192, 178.1, 137.1. Elemental analysis (C₁₉H₂₃NO₄): calculated: C, 69.28%; H, 7.04%; N, 4.25%; 0, 19.43%.

Example 8: (3-amino-5-isopropyl-2-methyl-1,4-benzoquinone (TQ8)

The compound of example 8 (TQ8) was obtained as dark violet crystals, yield 52.3%, mp 68-72° C.; IR (KBr, cm⁻¹): 3461 and 3328 (N—H₂), 2966, 1673 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.02 (6H, d, J=7.2 Hz) 1.69 (3H, s) 2.84 (1H, m) 6.25 (1H, d, J=1.2 Hz) 6.43 (2H, s, exchangeable with D₂O); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 8.97, 21.47, 26.3, 106.99, 132.37, 145.49, 149.54, 183.99, 185.41. EI-MS: m/z 179.2, 100% (M⁺), 164.1, 36.7%, 136.1, 62.4%, 108.1, 38.5%. Elemental analysis (C₁₀H₁₃NO₂): calculated C, 67.02%; H, 7.31%; N, 7.82%. Found: C, 66.65%; H, 7.15%; N, 7.81%.

Effects of Synthesized Compounds on Cancerous Cell Lines

Cellular Viability

Human lung cancer cells A549, human breast cancer cells MDA-MB-231 and colorectal cancer cells HT29, were used to test the antiproliferative activity of the synthesised compounds. Human lung cancer cells A549 were maintained in RPMI 1640 medium (Hyclone Laboratories, USA), human breast cancer cells MDA-MB-231 and colorectal cancer cells HT29 were maintained in DMEM medium (Hyclone Laboratories, USA). All media was supplemented with antibiotics (penicillin 50 U/ml; streptomycin 50 ug/ml) (Hyclone Laboratories, USA).

Cells were seeded at a density of 5,000 cells/well into 96-well plates. After 24 h, cells were treated for 24 and 48 h with different concentrations of compounds TQ1-5 and 8 (5-100 μM), in triplicate. Control cultures were treated with 0.1% DMSO. The effect of the compounds TQ1-8 on cell viability was determined using the CellTiter-Glo Luminescent Cell Viability assay (Promega Corporation, Madison, USA), based on quantification of ATP, which signals the presence of metabolically active cells. The luminescent signal was measured using the GLOMAX Luminometer system. Data were presented as proportional viability (%) by comparing the treated group with the untreated cells, the viability of which is assumed to be 100%.

The anticancer effects of the compounds were tested on human lung cancer cell line (A549), breast cancer cell (MDA-MB-231) and colorectal cancer cell lines (HT29) using cell viability assay.

FIGS. 1A and 1B show the effects of compounds TQ 1-5 and 8 on the cell viabilities of human lung cancer cell line, A549, using 5, 50 and 100 μM concentrations. Values are recorded relative to the control sample (DMSO).

Decreases in cellular viability of cancerous cells are observed with increasing drug concentration and time of exposure (24-48 hours). The six compounds at 100 μM concentrations gave steady decreases in cell viability after 24 hours by 15, 32, 29, 17, 33 and 99% relative to the control (DMSO), respectively. After 48 hours exposure, further decreases of 33, 57, 64, 58, 48 and 100% in cell viability were observed.

These results indicate a toxic effect against lung cancer cells for compounds TQ1-5 and TQ8. TQ8 had the highest toxic effect of the derivatives tested with cell viability close to zero relative to the control after 24 hours. Compound TQ8 was further tested on breast and colorectal cancer cell lines. All experiments were repeated at least three times.

FIG. 1B shows the effects of compound TQ8 on the cellular viability of MDA-MB-231 and HT29 cells over 24 and 48 hours using 5-100 μM concentrations. A concentration and time-dependent decrease in cell viability was observed. The losses in cell viability were 83% and 97% using 24 hours exposure at 100 μM concentrations. These losses increased to 98% and 99% after 48 hours exposure for MDA-MB-231 and HT29 cell lines, respectively.

Compound TQ8 showed the best potency among the eight synthesized thymoquinone derivatives against examined cancerous cell lines. A complete suppression of cell viability was observed at 48 hours using 100 μM. The relative cytotoxic effect of compound TQ8 on tested cancer cell lines was found in the following order A549>MDA-MB-231>HT29.

An IC50 gives a good estimate of the cytotoxic potency of different drugs against cancer cells. The IC50s (concentration produces 50% inhibition in cells viabilities) for compounds TQ1-5 and TQ8 at 24 hours are shown in Table 2.

The results ranged from 35.01-105.05 μM for tested thymoquinone derivative compounds against A549 cell line. TQ8 gave IC50s of 35.01, 45.14 and 55.81 μM against A549, MDA-MB-231 and HT29 cells, respectively. These results indicate good IC-50 values against the tested cells lines.

These results also indicate that compound TQ8 is ≥200% potent compared to the parent TQ molecule whose IC50 has been reported as 78.34 μM against A549 cells.

TABLE 2 IC50s of thymoquinone derivatives IC 50 (μM) Compound A 549 MDA 231 HT29 TQ 78.34 — — TQ1 74.32 — — TQ2 84.29 — — TQ3 83.19 — — TQ4 88.65 — — TQ5 105.05 — — TQ8 35.01 45.14 55.81

The cytotoxic effects for the compounds seen against the cancer cells indicate that the compounds could be suitable in the use of the treatment of cancers.

The compounds of the invention, TQ1-8, may be particularly good in in vivo models.

Interaction of G-Quadruplex DNA with TQ Ligands

Several mechanisms have been suggested for the anti-tumour effects of thymoquinone compounds. Stabilising the formation of G-quadruplex DNA structures with small molecules has been found to inhibit the telomerase enzyme found in active cancer cells, and has been seen as an effective approach for developing anticancer molecules. Therefore the thymoquinone derivatives were tested for their binding affinity and selectivity towards G-quadruplex DNA.

DNA solutions for use in the following assays were prepared as described below:

Calf Thymus DNA (Ct-DNA)

A 1000 μg/ml calf thymus ds-DNA was prepared by dissolving 10 mg of DNA (Sigma-Aldrich) into 10 ml Tris-KCl buffer, pH 7.4, without sonication or stirring. The solution was gently inverted overnight at 4° C. to completely solubilize the DNA and prevent shearing of the large genomic DNA. Resultant ct-DNA solutions are stable at 4° C. for several months.

Single Stranded DNA

Purchased synthetic nucleic acids primers (AlphaDNA, Canada) with human telomere sequence; 5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO: 1), its fluorescein labelled 5′ primer 5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO: 2) or its complementary strand 3′-TCCCAATCCCAATCCCAATCCC-5′ (SEQ ID NO: 3) were reconstituted by centrifugation for 10 min at 7000 rpm to collect the DNA into the vials' bottoms. A 2.00 ml Tris-KCl buffer, pH 7.4, was added to each vial, left 2 min for rehydration then vortexed for 30 seconds. Reconstituted primers were kept overnight at 4° C. before use. Stability of reconstituted primers is more than 6 months.

G-Quadruplex DNA

A 2 ml of the stock single stranded DNA; 5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO: 1) was gently heated up to 95° C., incubated for 10 minutes and then left to cool to room temperature. Resultant solution was kept in fridge at 4° C. overnight.

Hybridization of Telomeric DNA

A 10⁻⁴ M telomeric dsDNA was prepared by mixing equimolar amounts of 5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO: 1) (268.80 μL of 7.44×10⁻⁴M) and complementary strand 3′-TCCCAATCCCAATCCCAATCCC-5′ (SEQ ID NO: 3) (738.0 μL of 2.71×10⁻⁴ M). The solution was made up to 2 ml using KCl-Tris-Cl buffer, pH 7.4, vortexed for 15 seconds, incubated at 95° C. for 10 min and left to cool to room temperature. Resultant hybridized dsDNA was kept at 4° C. until use.

Concentrations of reconstituted stock DNA solutions were determined by diluting 10 μl of each solution to 1 ml using KCl buffer, pH 7.4. Solutions were vortexed for 15 seconds and its absorbance were measured at 260 and 280 nm. Concentrations were calculated using C(μg/ml)=A260×weight per OD×dilution factor, where A is the absorbance at 260 nm. The purity of oligonucleotides was estimated based on the ratio A260/A280. Ratios ≤1.8 were considered enough to indicate high purity. Since G-quadruplex DNA is formed by folding up from single strands, its concentration was similar to that of its single stranded DNA.

TQ Stability

The stability of the thymoquinone derivatives in Tris-KCl buffer, pH 7.4 at room temperature were investigated using UV-Vis spectrophotometry. Solutions were found stable and no change in absorbance for up to 12 hrs. However, decay in absorbance was observed when solutions kept for longer times. Therefore, freshly prepared solutions were used throughout.

To confirm an interaction between the thymoquinone derivatives and G-quadruplex DNA, this interaction was studied using fluorescence, fluorescence quenching and circular dichroism spectroscopies

Fluorescence Titration

To 3 ml of 5×10⁻⁵ M of each of compounds TQ1-8 in Tris-KCl-buffer, pH 7.4, successive portions of G-quadruplex DNA (1.44×10⁻⁴ M) were added. After each addition, the TQ solution was stirred for 20 seconds, incubated for 3 min and its emission was scanned in the range 300-600 nm using excitation Amax of 280 nm and slit width of 10.00 nm. Titration stopped when no change in fluorescence intensity was observed.

The results are shown in FIG. 2. Fluorescence titrations of compounds TQs 1, 2, 4, 5 and 7 with G-quadruplex DNA showed decrease in fluorescence intensity and red shifts by 24, 14, 30, 25 and 41 nm (FIGS. 2a, 2b, 2d, 2e and 2g ). Compounds TQ3 and TQ6 showed a hypochromicity and red shifts by 4 nm and the appearance of a new peak at 353.7 and 350 nm respectively (FIGS. 2c and 2f ). Compound TQ6 showed an isosbestic point at 315 nm. Compound TQ8 showed an increase in fluorescence intensity with slight red shift (FIG. 2h ). These changes in fluorescence spectra of TQs during titration indicated the binding of TQs with G-quadruplex DNA. The isosbestic point indicates an equilibrium process during binding interaction.

Quenching Assay of Fluorescein Labelled G-Quadruplex

Additional confirmation for TQ-G-quadruplex interactions was obtained through fluorescence quenching titration. The following assay was used to confirm binding interactions of TQ derivatives and their selectivity towards human telomeric G-quadruplex.

To 3 ml of 1×10⁻⁷ M fluorescein labelled G-quadruplex (5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′) (SEQ ID NO: 2), successive portions of each of the compounds TQs 1-8 (10⁻⁴ M) in Tris-KCl buffer, pH7.4, were added. After each addition, the solution was stirred for 20 seconds, incubated for 3 minutes and scanned for its emission spectra at the Fl-G-quadruplex emission Amax of 518 nm and excitation Amax of 494 nm.

Fluorescence intensity of Fl-G-quadruplex is quenched when a molecule binds it near the fluorescence labelling flag molecule.

The changes in fluorescence emission of 5′-fluorescein-labelled G-quadruplex DNA at 518 nm using 494 nm as the maximum wavelength of excitation are shown in FIG. 3. Fluorescence of 5′-fluorescein-labelled-quadruplex DNA showed a decrease in fluorescence intensity with successive addition of the thymoquinone derivative compounds. Quenching of 5′-fluorescein-labelled G-quadruplex is attributed to binding of the compounds in fluorescein proximity on Fl-G-quadruplex DNA.

Circular Dichroism Titration

CD spectroscopy was used to follow conformational change of G-quadruplex DNA upon interaction with the thymoquinone derivatives. To 1 ml G-quadruplex DNA (4×10⁻⁶ M) in Tris-KCL buffer, pH 7.4, successive amounts of each of the compounds TQ 1-8 (10⁻⁴ M) were added in ratios [drug]/[G-quadruplex] in the range of 0.2-15. After each addition, the solution was well shaken, incubated for 3 minutes at room temperature and scanned in the range 200-400 nm with 50 nm/min, band width 1 nm and 3 accumulations. Samples' CD were subtracted from the blank and then base line corrected. Changes in CD bands at 293 nm were recorded versus drugs' concentrations.

Interaction between the thymoquinone derivatives and G-quadruplex DNA was also tested by CD titrations. Change in CD intensity during titration has been used to estimate the binding mode between the ligand and DNA. A decrease in CD intensity during DNA titration with ligand has been correlated with an intercalation binding mode while an increase in intensity has been correlated with groove binding mode. Therefore, gradual decrease in CD intensity in the measurements may indicate an interaction mode between the derivative compounds and G-quadruplex.

FIG. 4 shows the CD titration spectra of G-quadruplex DNA with compounds TQ1-TQ8 (4a-h). Decreases in CD intensity, without changes in bands positions or shapes indicated a face n-n stacking intercalation process without conformational change in G-quadruplex during titration.

Melting Temperature Curves

In order to determine the stability of DNA upon complexation with ligand and its binding affinity, melting temperatures were determined.

Melting temperature curves for G-quadruplex and their TQs adducts were constructed using CD spectral measurements.

A 1 ml telomeric G-quadruplex (3.93×10⁻⁶ M) in Tris-KCl-buffer pH7.4, was heated in 1-5° C. increments in the range 25-95° C. using 5 minutes incubation time intervals. CD spectra were recorded in the range 200-400 nm using 50 nm/min, 1 nm band width and 3 accumulations at each point. CD spectra were baseline corrected against blank solution and CD intensities at 293 nm were plotted versus temperature.

Similarly G-quadruplex-TQ1-8 1 mL complex solutions that were 3.93×10⁻⁶ M of G-quadruplex and 3.93×10−6 M of TQs were heated up to 95° C. and measured. The solutions were prepared by mixing equi-molar amounts of G-quadruplex (27.3 μL, 1.44×10⁻⁴ M) with TQ compounds 1-8 (39.30 μL, 1×10⁻⁴ M) in 1 mL KCl-buffer, pH 7.4. CD spectra were baseline corrected and CD intensities at 293 nm were plotted versus temperature.

FIG. 5 shows the melting temperature curves for G-quadruplex and its TQs' complexes based on CD measurements. Table 3 shows the Tm values ranged between 70 and 91° C. for G-quadruplex DNA and its TQs complexes. These values reflected Δ Tm ranges between 6.0° C. and 21° C. Compound TQ8 showed the highest Tm (91° C.) which is 21° C. higher than the G-quadruplex DNA.

These values are consistent with the binding constants shown in Table 3 and indicate that the compounds of the invention act as stabilizers for G-quadruplex DNA.

Binding Affinity

Scatchard plots were used to determine the binding affinity of the thymoquinone derivative compounds to G-quadruplex based on fluorescence titration, keeping the compounds concentration constant and varying DNA amounts.

Non-linear Scatchard plots were obtained for all TQ derivatives suggesting more than one type of dependant binding sites for all TQs molecules on G-quadruplex DNA molecule. Dependant binding sites may have synergistic (the first bound ligand encourage the next binding one) or antagonistic (the first bound ligand suppress the next binding one) effects on each other, a phenomenon known as the neighbor exclusion effect. Non-linear regression based on a modified Scatchard equation gave the binding constants and number of binding sites shown in Table 3. Compound TQ8 has shown the highest binding constant (1.33×10⁷ M⁻¹) and compound TQ5 has shown the lowest binding constant (7.76×10⁴ M⁻¹)

TABLE 3 Melting temperatures (Tm), binding constants (K) and number of binding sites (n) of G-quadruplex DNA upon interaction with various TQ derivative compounds (TQ1-8). Complex Tm ° C. Δ Tm ° C. K (M⁻¹) N G-quadruplex DNA 70.0 0.00 — — G-quadruplex DNA- 79.0 9.0 1.13 × 10⁵ 2 TQ1 G-quadruplex DNA- 76.0 6.0 5.67 × 10⁵ 1 TQ2 G-quadruplex DNA- 76.0 6.0 3.30 × 10⁵ 3 TQ3 G-quadruplex DNA- 76.0 6.0 9.52 × 10⁴ 3 TQ4 G-quadruplex DNA- 77.0 7.0 7.76 × 10⁴ 1 TQ5 G-quadruplex DNA- 80.0 10.0 1.49 × 10⁶ 2 TQ6 G-quadruplex DNA- 77.0 7.7 1.17 × 10⁶ 2 TQ7 G-quadruplex DNA- 91.0 21.0 1.33 × 10⁷ 2 TQ8 Selectivity of TQs Towards G-Quadruplex

Selectivity of TQ derivative compounds towards G-quadruplex DNA was investigated using Fl-G-quadruplex (5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′) (SEQ ID NO: 2) in presence of the telomeric dsDNA or ct-DNA as interfering species.

A 3 mL solution of TQ1-Fl-G-quadruplex complex was prepared by mixing 30.00 μl of Fl-G-quadruplex (10⁻⁵ M) with 30 μl of TQ1 compound (10⁻⁵ M). The solutions was made up to 3.00 ml using Tris-KCl-buffer pH 7.4, vortexed for 10 seconds, incubated for 3 minutes and then scanned for its fluorescence in the range 500-700 nm. The solution was then mixed with 0, 10, 50 or 100 folds of telomeric dsDNA or ct-DNA, vortexed for 10 seconds, incubated for 30 minutes at room temperature and scanned for its emission spectrum in the range 500-700 nm. The procedure was repeated for the TQ2-TQ8 compounds.

FIG. 6 shows change in fluorescence intensity of 5′-Fl-G-quadruplex TQs complexes in presence of 0, 10, 50 and 100 folds of ctDNA (FIG. 6a ) and telomere dsDNA (FIG. 6b ). The figures show that the fluorescence of 5′-Fl-G-TQs complexes are either constant or a slightly increased upon addition of ctDNA or telomere dsDNA indicating that both DNA species are non or slightly-interfering. These experiments indicate good selectivity for investigated thymoquinone compounds towards G-quadruplex DNA over ctDNA and telomere dsDNA.

These results indicate that the thymoquinone derivatives of the invention show good selectivity towards G-quadruplex DNA over duplex DNA and cytotoxicity over cancer cells, thereby suggesting that the compounds would be helpful in the treatment of cancers. 

The invention claimed is:
 1. A compound of formula (I)

or a pharmaceutically acceptable salt or solvate thereof, wherein R₁ and R₂ are selected from CH₃ and isopropyl, wherein R₁ and R₂ are different; X is NR₃R₄, wherein: R₃ is selected from H or —(CH₂)₂—OH; and R₄ is selected from H or —(C₁-C₄alkyl)R₅, wherein: R₅ is selected from: a) —OH, b) phenyl substituted by 1-3 substituents independently selected from —CF₃, —F, —OCH₃, —NH₂ and —SO₂NH₂, c) a 5 or 6 membered heterocyclic ring having 1 or 2 hetero atoms selected from O and N, and wherein the heterocyclic ring is optionally substituted by 1-2 substituents independently selected from —OH and CH₃, d) a ring system having the formula of:

and e) NR₆R₇, wherein: R₆ is selected from H or CH₃; and R₇ is selected from CH₃, phenyl, and a ring system having the formula of:

wherein the ring system is optionally substituted by 1-2 substituent of CH₃; and Y is H, wherein R₃ and R₄ are not both H.
 2. A pharmaceutical composition comprising the compound of formula (I) according to claim 1 and a pharmaceutically acceptable diluent or carrier, wherein the pharmaceutical composition is in the form of a tablet, capsule, pill, powder, solution, suspension, or emulsion.
 3. The compound of claim 1, wherein R₃ is H.
 4. The compound of claim 1, wherein R₄ is (C₁-C₄alkyl)R₅ and R₅ is selected from: a) —OH, b) phenyl substituted by 1-3 substituents independently selected from —CF₃, —F, —OCH₃, —NH₂ and —SO₂NH₂, c) a 5 or 6 membered heterocyclic ring selected from morpholinyl, pyranyl, piperidinyl, pyrrolidinyl, piperazinyl, pyridinyl, and pyrimidinyl, wherein the heterocyclic ring is optionally substituted by 1-2 substituents independently selected from —OH and CH₃, d) a ring system having the formula of:

and e) NR₆R₇, wherein: R₆ is selected from H or CH₃; and R₇ is selected from CH₃, phenyl, and a ring system having the formula of:

wherein the ring system is optionally substituted by 1-2 substituent of CH₃.
 5. The compound of claim 1 wherein R₄ is H or —(C₁-C₂alkyl)R₅, wherein R₅ is selected from OH, morpholinyl and phenyl substituted with 1 or 2 substituents selected from —CF₃, —F and —OCH₃.
 6. The compound of claim 1, wherein R₁ is CH₃ and R₂ is isopropyl.
 7. The compound of claim 1, wherein the compound is selected from the group consisting of: 5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone; 5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone; 5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone; 5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone; 5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone; and 5-isopropyl-2-methyl-3-(3,4-dimethoxylbenzylamino)-1,4-benzoquinone. 